The present invention relates to hand impact tools. It is particularly applicable to tools that are to be flexible in one direction but rigid in the other.
A significant advance in the field of hand impact tools was provided by the invention described in U.S. Patent Application Ser. No. 056,721 of Whiteford. The hammer described in that application includes a column of vertebra members extending from the handle to the head. Two shafts extend through the column from the handle to the head, one of which is free at least at one end and permitted to move with respect to the vertebra members in the column. The other column is fixedly attached at both ends. The resultant structure flexes in one direction when the head hits a workpiece, but it remains rigid when the claw side of the hammer is used. It is also believed that the use of a multiplicity of vertebra members enhances the shock absorption afforded by the flexible handle.
It is necessary in order to prevent flexing during use of the claw that the vertebra members be substantially incompressible, but flexing of the Whiteford hammer typically results in compressive force on the vertebrae in the region of the fixed shaft, and the opposing force from the vertebrae tends to oppose the desired flexing when a workpiece is struck. Some opposition to flexing is desirable, of course, so the shaft size would ordinarily be designed so that the sum of the resistances offered by the shaft and by the vertebra members would equal whatever level of resistance is desired. However, the resistance offered by the vertebra members limits the size of the shaft that can be used, and strength considerations sometimes make an increase in shaft size desirable.
It is accordingly an object of the present invention to maintain the advantages of the vertebra members while reducing the opposition to flexing incurred by their use. It is a related object to permit the use of larger-sized shafts in tools of this type.